In a mobile communication system, in order to meet a requirement on mobility, after establishing a connection with a network in a cell, the UE still needs to measure the quality of the signals of its neighboring cells to select a proper cell for handover. Taking an Evolved Universal Terrestrial Radio Access Network (EUTRAN) as an example, the specific process of the measurement of a UE in a connected state is as follows:
the network sends a measurement control message to the UE, wherein the measurement control message contains a Measurement Identity (MID), an event type, a measurement object, and an attribute to be measured;
the UE initializes parameters according to the MID in the measurement control message and acquires the attribute and measurement result of each of all measurement objects in the measurement control message;
the UE performs event evaluation on the measurement result of each measurement object according to the initialized parameters or a preset threshold, and determines, through the evaluation, the measurement object in all measurement objects which meets a condition that the period during which a triggering condition for an measurement event is met is greater than or equal to the length of a preset Time To Trigger (TTT);
the UE places these measurement objects meeting the event triggering condition (the measurement objects refer to corresponding cells at this moment) in the cell list (cellsTriggeredList) of the MID corresponding to the event; and
the UE generates a measurement report according to the measurement result of the determined measurement objects and sends the measurement report to the network, the measurement objects contained in the measurement report are all acquired from the cell list of the MID corresponding to the event.
In a mobile communication system, a measurement configuration comprises an MID, a measurement object, the form of measurement reporting (e.g. event-triggered reporting or periodical reporting), etc, wherein the measurement object takes a frequency or a set of cells on a frequency as a unit. An MID corresponds to a certain measurement object and a specific measurement reporting configuration which means a reporting attribute, and different measurement reporting configurations of the same measurement object correspond to different MIDs. For a type of event triggered measurement configuration, there is one-to-one mapping between a measurement reporting configuration and a measurement event (at this moment, one MID describes one measurement object and one measurement event corresponding to the measurement object). The currently-defined measurement event generally comprises the triggering condition, the leave condition, the specific threshold (Thresh), the hysteresis parameter Hys and the offset of the event and the duration of the triggering condition for the event.
To meet the requirement of a UE in a connected state on mobility, the UE is required to measure neighboring cells and report the measurement objects that meet the triggering condition for an event. At present, some measurement events have been defined for neighboring cells, for instance, a triggering condition for a measurement event is defined as that the signal quality of a neighboring cell is higher than a certain threshold, or that the signal quality of a neighboring cell is a specific offset higher than that of the current serving cell.
For an event-triggered measurement reporting, there are two ways of reporting: 1, single event-triggered reporting (or called even-triggered measurement reporting); 2, periodical event-triggered reporting. The single event-triggered reporting means that a network configures an event triggering condition for a UE, after performing detection and evaluation and determining that a measurement object meets the event triggering condition, the UE places the measurement objects meeting the event triggering condition in a cell list of the MID corresponding to the event, and the measurement report is only reported once, wherein the measurement objects contained in the report are all acquired from the cell list. If there are new measurement objects meeting the event triggering condition later, the UE will place the new measurement objects in the cell list of the MID corresponding to the event, and report the new measurement report, the measurement objects contained in the new measurement report are all acquired from the cell list at this moment, and the report is still only reported once.
Periodical event-triggered reporting means that a network configures an event triggering condition for a UE, after performing detection and evaluation and determining that a measurement object meets the event triggering condition, the UE places the measurement objects meeting the event triggering condition in a cell list of the MID corresponding to the event, wherein the measurement report is reported many times, the number of times of the reporting and the time interval of the reporting are both configured by the network, and the measurement objects contained in the measurement report reported every time are all acquired from the cell list currently reported. During or after many times of reporting, if there are new measurement objects that meet the event triggering condition, the UE will reset the number of reporting times, place the new measurement objects in the cell list of the MID corresponding to the event, and orderly report the measurement results again according to the reset number of reporting times and a set time interval. The measurement objects contained in each measurement report are acquired from the cell list currently reported.
A network may also configure, for a UE, periodical measurements to report the strongest cells (reportStrongestCells), in this case, the UE needs to report, at a certain time, the first several cells with the strongest signal quality measured at a certain frequency. As limited by the maximum number (maxReportCells) of the reported cells, the UE reports the first maxReportCells cells with the strongest signal at this frequency every time. The value of maxReportCells is configured by the network.
As regards the measurement on a measurement object, different systems use different measurement methods, all of which reflect the signal quality of a cell. In a Long Term Evolution (LTE) system, a UE measures Reference Signal Received Power (RSRP for short, taking dBm as unit), or Reference Signal Received Quality (RSRQ for short, taking dB as unit). In WCDMA, a UE measures the Received Signal Code Power (RSCP for short, taking dBm as unit) of a common pilot channel) or the Ec/No (taking dB as unit) of a common pilot channel. A UE needs to compare the measurement results of the same type when comparing the signal qualities of different cells. When it is evaluated that a measurement object meets an event triggering condition, a complete description on the measurement object comprises not only the RSRP or RSRQ measured by the UE but also the frequency specific offset (Ofn) of the measurement object and a cell specific offset (Ocn). Taking the A4 event defined in an LTE as an example: the signal quality of a neighboring cell is higher than a threshold, the specific mathematic expression is Mn+Ofn+Ocn−Hys>Thresh, wherein Mn represents the RSRP or RSRQ of a neighboring cell measured by the UE.
In the construction of a modern radio network system, indoor coverage is of the highest importance. A suitable indoor coverage scheme can, on the one hand, maximize the effect of a network and create greater value for operators, and on the other hand, greatly reduce the network construction cost of operators to achieve the goal of “high return with low investment”. On this ground, a radio access equipment called Home NB is developed. A home NB, as a resource dedicated to private subscribers, is deployed in private places such as families, groups, companies or schools to provide subscribers with various high-speed radio access services as well as a discount in charges and solve the problem of insufficient coverage of the existing distributed cellular radio communication system.
At present, there are three access modes for a Home NB: open mode, closed mode and hybrid mode. In the open mode, a Home NB allows the access of all subscribers, in this case, the Home NB cell is a macro cell. In the closed mode, a Home NB only allows the access of authorized subscribers, e.g. family members, group members, etc., which are referred to as a Closed Subscriber Group (CSG). Authorization information is saved in a Universal Subscriber Identity Module (USIM) of a UE. In the hybrid mode, a Home NB allows the access of all subscribers, and provides priority or discount for subscribers of the CSG. A cell covered by a macro NB (NodeB or eNodeB) is called a macro cell, while a cell covered by a Home NB is called a CSG cell with a CSG ID (Identity). A UE determines whether a CSG cell allows its access by determining the access mode of a Home NB to which the CSG cell belongs and/or information contained in an allowed CSG list saved in a USIM. For a specific UE, the number of the accessible CSG cells is generally limited, so the UE can locally save the information of CSG cells which has been accessed by the UE, which is called footprint information, and with the footprint information, the UE can enter a CSG cell accurately and quickly during a re-selection and handover.
A Home NB can use a dedicated frequency resource reserved by an operator, which is called a CSG dedicated frequency, or use a frequency resource identical to frequency resource used by a macro NB, which is called a mixed frequency. Cells with the same frequency are differentiated by a Physical Layer Identity (PCI). When a Home NB and a macro NB use the same frequency, the operator will specifically reserve a PCI resource (PCI split) for the Home NB, wherein a CSG cell uses the PCI in the PCI split. Like a macro cell, a CSG cell has a PCI and a Cell Global Identifier (CGI). As the number of physical layer identities are limited, with the increasing deployment of Home NBs, a PCI cannot uniquely represent one CSG cell, while a CGI is unique in the range of a Public Land Mobile Network (PLMN), a UE and a macro NB can uniquely determine a CSG cell only after acquiring a CGI.
With the increasing deployment of Home NBs, the handover of a UE between a macro cell and a CSG cell or between CSG cells is inevitably required to meet the requirement on mobility. As a kind of plug-and-play device with mobility, Home NBs are deployed in large number, typically, no neighbor relationship is configured between a macro cell and a CSG cell, that is, a UE cannot acquire the information of a neighboring CSG cell when handing over from a macro cell to a CSG cell, and a UE needs to make a real-time detection to acquire the CSG ID, the CGI, the TAC (Tracking Area Code), the PLMN of a CSG cell and other information to achieve the purpose of handover. At the same time, as a UE can enjoy a priority or discount in some authorized CSG cells, a UE needs to be handed over to a suitable CSG cell as soon as possible.
In an idle state, a UE automatically searches for suitable CSG cells on a mixed frequency or a dedicated frequency that are not configured in a system message; in a connected state, a UE also needs to automatically search for accessible CSG cells on a mixed frequency or a dedicated frequency. However, according to the existing protocol, a UE cannot evaluate a CSG cell that is not on a mixed frequency or a dedicated frequency in a measurement configuration. At the same time, due to the limitation on the format of a measurement report, a UE cannot report a CSG cell that is not on a mixed frequency or a dedicated frequency in a measurement configuration. However, if a network configures, for a UE, a measurement configuration on a dedicated frequency, using the existing reporting mechanism by the UE will cause many useless measurement reports, because the CSG cells inaccessible to the UE may be reported in the measurement reports, and the performance of the network will be seriously affected by these useless measurement reports, this problem will cause a UE in a connected state cannot access a CSG cell smoothly and preferentially.